History
A 5-year-old sexually intact male Welsh Corgi was evaluated for progressive ambulatory paraparesis of the pelvic limbs of approximately 9 months' duration. Bilateral pelvic limb ataxia and paresis had been noticed by the owner during the 9 months prior to referral. There was no history of trauma, and the dog did not have signs of pain. On physical examination, conscious proprioception in the pelvic limbs was absent, the patellar reflexes were exaggerated, severe wear was evident on the toenails of each pelvic limb, and the dog's body condition was thin. The neurologic lesion was localized to the area from vertebrae T3 through L3. No abnormalities were detected on plain radiographs of the vertebral column, and results of CSF analysis were considered normal. Myelography was performed (Figure 1).
Lateral (A) and ventrodorsal (B) myelographic views of the thoracic portion of the spinal cord in a 5-year-old dog evaluated for progressive paraparesis of the pelvic limbs of approximately 9 months' duration.
Citation: Journal of the American Veterinary Medical Association 228, 7; 10.2460/javma.228.7.1019
Determine whether additional imaging studies are required, or make your diagnosis from Figure 1—then turn the page
Same lateral myelographic view as in Figure 1 (enlarged). Notice pooling of the contrast medium in the dorsal subarachnoid space and subsequent termination of the contrast column over the T10 vertebral body (arrow).
Citation: Journal of the American Veterinary Medical Association 228, 7; 10.2460/javma.228.7.1019
T1-weighted axial magnetic resonance image of the thoracic portion of the vertebral column of the dog in Figure 1. The spinal cord is compressed by a dorsal hypointense lesion (arrow).
Citation: Journal of the American Veterinary Medical Association 228, 7; 10.2460/javma.228.7.1019
Diagnostic Imaging Findings and Interpretation
Pooling of the contrast medium in the dorsal subarachnoid space and subsequent termination of the contrast column are evident over the T10 vertebral body (Figure 2).
Comments
Magnetic resonance imaging (MRI) was performed before and after IV administration of gadodiamide (13 mg/kg [5.9 mg/lb]). A hypointense region dorsal to the spinal cord over vertebral bodies T9 and T10 was detected on axial and sagittal T1-weighted images (Figures 3 and 4). On T2-weighted images, the corresponding area was hyperintense and compatible with a fluid-filled structure. Contrast enhancement was not detected after administration of gadodiamide.
On the basis of results of myelography and MRI, an arachnoid cyst was diagnosed; the diagnosis was confirmed during surgery. A dorsal hemilaminectomy of the T9 and T10 vertebral bodies was performed. Bulging of the dura mater was apparent in this region, and when the dura mater was incised, the appearance of the CSF was considered normal. The dura mater was excised throughout the entire laminectomy site.
Spinal arachnoid cysts that cause neurologic deficits are not common in dogs. The term arachnoid cyst is misleading because an arachnoid cyst does not have a true epithelial lining.1 An arachnoid cyst is an intradural, extramedullary diverticulum of the subarachnoid space and is separated from the spinal cord by an intact pia mater.
The underlying cause of arachnoid cysts is not known. Proposed causes include congenital malformation, trauma, inflammation, or neoplasia.2 In the dog of this report, histologic examination of the arachnoid cyst revealed minimal histiocytic and lymphocytic inflammation with unremarkable dense connective tissue. The pathogenesis was not identified.
Spinal arachnoid cysts can usually be diagnosed via myelography. The characteristic myelographic findings include pooling of the contrast material in the subarachnoid space or possible sudden termination of the contrast column.3 Magnetic resonance imaging can be helpful in determining the exact location and extent of a cyst for surgical removal. Additionally, spinal cord atrophy and syringohydromyelia may be detected with MRI; T1-weighted images provide the best delineation of the lesion.4
Surgical resection and decompression have provided the best outcome in animals with arachnoid cysts. Complete resection of an arachnoid cyst can be technically difficult; therefore, marsupialization of the dura mater is recommended to help prevent recurrence.5 The prognosis is good; however, patients may require several weeks or months before appreciable improvement in clinical signs is seen, and neurologic deficits may persist.3 Clinical signs of the dog in this report had improved by the time of hospital discharge. The dog was ataxic; however, its conscious proprioception was considered normal.
T1-weighted sagittal magnetic resonance image of the thoracic portion of the vertebral column of the dog in Figure 1 obtained at the level of the T10 vertebral body. The cyst (arrow) is hypointense to the spinal cord parenchyma.
Citation: Journal of the American Veterinary Medical Association 228, 7; 10.2460/javma.228.7.1019
- 1.↑
Bagley RS, Britt LG, Cambridge AJ, et al. Radiographic diagnosis: arachnoid cyst in a dog. Vet Radiol & Ultrasound 1997;38:434–436.
- 2.↑
Munana KR, Olby NJ, Sharp NJ, et al. Spinal arachnoid cysts in 17 dogs. J Am Anim Hosp Assoc 2003;39:271–282.
- 3.↑
Dewey CW. Myelopathies: disorders of the spinal cord. In: Dewey CW, ed.A practical guide to canine and feline neurology. Ames, Iowa: Iowa State Press, 2003;313–314.
- 4.↑
Rylander H, Lipsitz D, Berry W, et al. Retrospective analysis of spinal arachnoid cysts in 14 dogs. J Vet Intern Med 2002;16:690–696.
- 5.↑
Grandy JL, LeCouteur RA. Diseases of the spinal cord. In: Ettinger SJ & Feldman EC, eds. Textbook of veterinary internal medicine. 5th ed. Philadelphia: WB Saunders Co, 2000;608–653.
